Tuesday, 3 November 2009

River Red Gumlets

The iconic Australian riverbank tree, Eucalyptus camaldulensis, grows in every state and territory in mainland Australia, extending across five million square kilometres of the country. First named from a specimen growing in Italy, Australian botanists have now split the species into seven subgroups.

The species name doesn’t change, as these new subgroups have been given ‘subspecies’ names – all of them shorter, and mostly rolling off the tongue a little easier than camaldulensis!

But before I thrill you with the minutiae of this taxonomic fine-tuning, a little more about the species itself. According to the authors (McDonald, Brooker and Butcher) of this paper in Australian Systematic Botany, the River Red Gum was one the first eucalypts to be grown overseas and is perhaps now the most widely planted of any eucalypt species. Fast growing and tolerant of a wide range of climates and soils, it is particularly good for countries with long dry seasons

The story of how it came to be named from a plant growing in Italy is surprisingly vague. I mentioned in a recent posting that the garden in question was in Camalduli, near Naples, but no know quite knows how the plant got to Italy and fully mature by 1832.

The authors of this recent article speculate that because the species doesn’t grow east of the Great Dividing Range, where the first Europeans settled in 1788, seed was most likely collected on the French expeditions of d’Entrecasteaux or perhaps Baudin. There are historical reports suggesting the seeds came to Italy via France.

But that’s all history. Now there are seven new River Red Gums. As the authors note, the distinguishing characters are relatively subtle and may be difficult to use. Examples are the density of the vein network (reticulation) on the leaves, and the arrangement of the male parts (stamens) in the flower bud. Other characters include the presence and shape of a ‘beak’ on the bud cap, the colour of leaves, and the type of bark

Still, if you live in Victoria the changes are easy – there aren’t any, except for having to add ‘subspecies camaldulensis’ at the end of the name each time you write it down. In New South Wales we have three of the subspecies – Queensland has the most, I think, with four.

In brief, camaldulensis is constrained mostly to the Murray-Darling basin, acuta scattered through Queensland and extending just into the north-east of New South Wales, arida as the name suggests restricted mostly to inland Australia but almost reaching the coast in Western Australia, minima north of Adelaide, simulata the far north of Queensland, obtusa all across the north of Australia, and refulgens in the middle-west of Western Australia.

There are some intergrades between these entities, but that’s partly why they are sub, and not full, species.

Image: One of Murray Fagg's beautiful plant portraits - this is a River Red Gum growing at Coopers Creek near Innamincka in South Australia (from website). I'm assuming it is subspecies arida.